The present invention relates to improvements in disk screens for screening or classifying wood chips in a paper machine.
Disk screens are desirable apparatus for screening or classifying discrete materials such as paper pulp, municipal wastes, and the like, such screens comprise a screening bed having a series of corotating spaced parallel shafts each of which has a longitudinal series of concentric screen disks which interdigitate with the screen disks of the adjacent shafts. Spaces between the disks permit only material of acceptable size to pass downwardly through the rotating disks bed, and since the disks are all driven to rotate in a common direction from the infeed in end of the screen bed to the outfeed or discharge end of the bed, the particles of material which are larger than the acceptable sizes of material will be advanced on the bed to the outfeed end of the bed and rejected.
Screening devices for the screening of wood chips incorporating parallel rotating shafts with interdigitated disks thereon have been known and various developments have been made including arrangements for the improved mounting of disks on the shaft such as, for example, disclosed in my copending application, Ser. No. 724,098, filed Apr. 17, 1985, which issued Mar. 31, 1987, as U.S. Pat. No. 4,653,648.
Difficulty has been encountered in existing disk screens. One problem which exists is that the volumes of flow which have to be accommodate tend to carry over acceptable material that should pass through the screen. With increases in sizes which are necessary to handle large volumes of flow, the screens generally consume substantial building space to process the required volume of material. Changes in design which include the arrangement of shafts oriented perpendicular to the material flow allow a substantial lower quantity of acceptable chips to pass over the screen, but because of the aggressive nature of the structure, over-thick chips pass through with the accepts lowering over-thick removal efficiencies.
It is accordingly an object of the present invention to provide an improved structure and method for disk screening of chips.
A further object of the invention is to provide an improved screen wherein the operating efficiency is improved and horsepower input consumption is reduced.
A further object of the invention is to provide a disk screen arrangement wherein removal efficiencies are improved in spite of heavy deliveries of material and with short retention time of material on the screen surface.